An msnbc.com study showing the Callaway Nuclear Power Plant faces the least risk from damage from an earthquake of all 104 U.S. nuclear plants has been disavowed by the U.S., Nuclear Regulatory Commission (NRC).

Lara Uselding, a NRC spokeswoman, said the NRC does not rank plants based on risk of damage from an earthquake.

Uselding said MSNBC reached its own conclusions in its rankings and the NRC did not approve the rankings.

“It was an incomplete report on the overall research that had been done by the NRC. Somebody at MSNBC took numbers and threw them together to create the rankings. We have said that is not accurate because the NRC does not rank plants by seismic risk,” Uselding said.

She said the NRC did do a study on earthquakes in 2008 to update a previous 1982 study of recent seismic activity but the NRC did not rank each plant for seismic risk.

“We did a generic issue 199 safety risk assessment. The objective of that was to perform a conservative screening level assessment to evaluate further investigations of seismic activity of Central and Eastern United States,” Uselding said.

“We continue to say, even after what has been going on in Japan that all operating nuclear plants in the United States remain safe and there is no need for any immediate action and that of course includes the Callaway Nuclear Power Plant. All nuclear plants in the United States are built to withstand the most severe natural threats recorded for that area. Even plants that are not in areas of heavy seismic activity are designed for safety in the event of a seismic disaster. Then we add a margin of error on top of that to make sure the plant is safe,” Uselding said.

Uselding said nuclear plants are not engineered based on earthquake Richter Scale probabilities. “It’s actually based on probable and previous ground motion and shaking. Plants are planned with safety related systems and reactor analysis,” Uselding said.

Mike Cleary, an Ameren Missouri spokesman, said he had heard about the MSNBC study and was excited to learn that the Callaway plant was ranked as the least likely to be damaged by an earthquake. But when he contacted the NRC about the study, he was told the study was not valid because the rankings were done by MSNBC, not the NRC.

Cleary said that does not affect the fact that the plant was built to be safe and still is safe. He noted the New Madrid fault is 200 miles away from the Callaway Nuclear Power Plant. He said the plant was built specifically not only to meet but also to exceed the likely earthquake activity for this area as well as tornadoes and other threats.

“The plant’s safety design is not tied to the Richter Scale. The same magnitude of earthquake on the Richter Scale could have a totally different impact on the nuclear plant, depending upon the type of soil present at a particular area. It is based on the geology of the Callaway Nuclear Plant site itself when the specific standards were developed for this plant,” Cleary said.

MSNBC reported it did the rankings based on information provided by the NRC.

The MSNBC study showed the odds of an earthquake damaging the nuclear reactor at the Callaway County nuclear plant are only one in 500,000 each year compared to the least safest plant with odds of one in 10,000 located near New York City.

The MSNBC study showed that nuclear plants that were near heavy seismic activity were built much stronger than plants that are not near earthquake areas of the nation.

Rick Eastman, supervisor of business operations at the Callaway Nuclear Power Plant, said the plant was built to meet worst case scenarios regarding seismic activity or tornadoes.

Bill Dedman, who wrote the msnbc.com report, issued the following statement:

"Our msnbc.com story made clear that the NRC does not rank the nuclear plants. But it does publish its estimates for each plant, by which we ranked the plants.

"If the newspaper starts publishing the American League East standings in alphabetical order, it's entirely appropriate for the reader to put the teams in order by winning percentage.

"Don't be misled by the NRC's non-denial denial. NRC hasn't said our numbers are wrong. I checked my interpretation with Scott Burnell in Public Affairs, who checked with the NRC technical staff before publication. No challenge from NRC has arrived after publication.

"After all, they're NRC's numbers.

"What NRC is saying is that it doesn't do rankings. That's right. We did, from NRC's data. Just as the story says.

"You can see for yourself in the NRC report that:

"-- NRC says the risk of quakes in the central and eastern states is higher than previously thought.

"-- It still thinks plants are safe.

"-- but their margin of safety is reduced.

"-- and some plants are now near the point where they should be re-examined, and perhaps retrofitted.

"-- and the staff says this should now move from being a research issue to a regulatory issue.

"-- and it has made its best estimates of the frequency (chance, odds) of an earthquake that would cause core damage to a plant.

"A link to the NRC report is on the msnbc.com report: http://www.msnbc.msn.com/id/42103936/ns/world_news-asiapacific/."